The studies add to a growing body of evidence about the role of diet in cancer. Cancer experts now believe that up to two-thirds of all cancers come from lifestyle factors such as smoking, diet and lack of exercise.

The mothers of some of the women also were available to answer questions about what they fed their daughters as children. The women who ate the most soy-based foods such as tofu and miso when aged 5 to 11 reduced their risk of developing breast cancer by 58 percent, the researchers found.

It is not clear how soy might prevent cancer, although compounds in soy called isoflavones have estrogen-like effects.

A second study presented at the meeting showed that men who ate fish five times a week or more had a 40 percent lower risk of developing colorectal cancer compared with men who ate fish less than once a week.